Crossbow Bow Of The Crossbow
The crossbow bow of the crossbow differs from the classical one in that it has at least twice or even three times the reported speed of the arrow. Block bow is always more powerful and faster than a classical or recursive bow (with the same tension of the string and the fabrication of the shoulders). The difference is that "compounds" - block bows work not only with the strength of elastic elements - the shoulders. The force of the shot they provide is the same as on its predecessor - a recursive bow.
But the initial speed of the boom depends mainly on the special eccentric blocks located on the upper extremities of the shoulders, connected together by a system of cables for synchronous operation. This system of blocks and cables allows to disperse the bowstring (and, accordingly, the arrow) to high speeds.
The system of blocks, in fact - a system of levers, due to which due to the reduction of the force transferred to the string increases the speed of its movement. At the very end of the drawstring, the blocks provide a significant reduction in the force required to hold them. These include the complexity and bulkiness of the design, its greater weight (compared with the recursive bow), a half or two times longer string (and, consequently, a longer bed), more stringent requirements for the accuracy and reliability of the parts being manufactured.
Fasten the bowstring to the bow of the crossbow
You can fasten the bowstring on a crossbow bow in various ways. One of them is the use of blocks. The block consists of a bearing on which a ring with a groove for the bowstring protruded in it is put on. The bearing rotates freely around the axis fixed to the end of the arm. The axle is also worn with pieces of metal, to which the bowstring is attached.
The simplified scheme without a bearing proved to be a good one. The end of the bowstring is fixed around one of the axes, then the bowstring goes along the groove of the opposite ring, fits into it, returns to the original axis, is wound around the ring groove and finally fixed on the opposite axis (Figure 2). What is the use of this design?
Firstly, two blocks and a 3-fold long bowstring give a gain in strength. Pull this bow several times easier. Secondly, after lowering the trigger, the bowstring will slide 1.5-2 times faster on the surface of the bed. This means that the initial speed of the arrow will increase by the same amount. Do your own conclusions. When designing, the main difficulty is how to attach blocks to the ends of the bow (Figure 3).
Shoulders of modern crossbows
Luke or, more correctly, the shoulders of modern top crossbows are made of a wide variety of materials: steel, aluminium, fibreglass laminate, composite materials, carbon. The most well-known are the shoulders of the composite, which is a multi-layer structure of fibreglass and carbon fibre.
The fibreglass structure of the shoulders gives them high energy intensity, and the carbon fibre reinforces properties. The shape of the shoulders, depending on the purpose, can be either direct or recursive, that is, with a characteristic onion-like curve. Crossbow shoulders on the ends have so-called endings - seats for the bowstring. The big advantage of the last generation's shoulders is their "fatigue" - they retain the stability of their characteristics even after several thousand shots.
